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A boarding school outbreak of pertussis in adolescents: value of laboratory diagnostic methods

Published online by Cambridge University Press:  09 December 2004

P. HORBY ,
C. R. MACINTYRE ,
P. B. McINTYRE ,
G. L. GILBERT ,
M. STAFF ,
M. HANLON ,
L. G. HERON ,
M. CAGNEY  and
C. BENNETT
P. HORBY
Affiliation:
Communicable Disease Surveillance and Response, World Health Organization, Ha Noi, Viet Nam National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, The Children's Hospital at Westmead and the University of Sydney, New South Wales, Australia
C. R. MACINTYRE
Affiliation:
National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, The Children's Hospital at Westmead and the University of Sydney, New South Wales, Australia
P. B. McINTYRE
Affiliation:
National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, The Children's Hospital at Westmead and the University of Sydney, New South Wales, Australia
G. L. GILBERT
Affiliation:
Centre for Infectious Diseases and Microbiology, Institute of Clinical Pathology and Medical Research, Westmead Hospital, Westmead, New South Wales, Australia
M. STAFF
Affiliation:
Northern Public Health Unit, NSW Health, Australia
M. HANLON
Affiliation:
Department of Immunology, Children's Hospital at Westmead, NSW, Australia
L. G. HERON
Affiliation:
South Western Sydney Public Health Unit, NSW Health, Australia
M. CAGNEY
Affiliation:
National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, The Children's Hospital at Westmead and the University of Sydney, New South Wales, Australia
C. BENNETT
Affiliation:
Northern Public Health Unit, NSW Health, Australia
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Abstract

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Culture for Bordetella pertussis (B. pertussis) is the traditional gold standard for laboratory diagnosis of pertussis but is insensitive, especially later in the course of illness and in vaccinated persons. Interpretation of serology is limited by the lack of an appropriate reference standard. An outbreak of pertussis in a crowded boarding-school dormitory allowed evaluation of laboratory correlates of infection. Questionnaires, serum samples and throat swabs were collected from members of the exposed group. Serum samples from unexposed controls of a similar age group were used for comparison. B. pertussis PCR was performed on throat swabs, and sera were tested for IgA antibodies against whole-cell (WC) B. pertussis antigen and IgG antibodies to pertussis toxin (PT). The Centers for Disease Control and Prevention definition for pertussis was used to define clinical cases. We evaluated the use of a previously published cut-off for PT IgG of 125 EIA units (EU)/ml. Completed questionnaires were obtained from 115 students, of whom 85 (74%) reported coughing symptoms, including 32 (28%) who met the clinical case definition for pertussis. B. pertussis was detected by PCR in 17 (15%) and WC IgA in 22 (19%) students; neither correlated with symptoms, but dormitory of residence strongly predicted PCR status. The mean PT IgG geometric mean concentration, in this situation of high pertussis exposure, correlated with severity of symptoms and was significantly higher in both symptomatic and asymptomatic children exposed during the outbreak (P<0·001) than in control children. A cut-off for PT IgG of 125 EU/ml was too high in an outbreak situation to be sensitive enough to identify pertussis cases. A case of pertussis in a crowded boarding-school dormitory resulted rapidly in an outbreak. Serology and PCR were useful in identifying the outbreak and commencing disease control measures. The use of serology has mostly been evaluated in community serosurveys, where it is not possible to determine if immunity reflects vaccination, asymptomatic disease or symptomatic disease. This outbreak gave us the opportunity to evaluate the value of serology and PCR in the presence of confirmed exposure to pertussis.

Type
Research Article
Information
Epidemiology & Infection , Volume 133 , Issue 2 , April 2005 , pp. 229 - 236
Copyright
© 2004 Cambridge University Press